JPH02183702A - Dust dispersion prevention device of black liquor recovery boiler - Google Patents

Abstract

PURPOSE:To burn a black liquor always at the most appropriate condition and reduce greatly the quantity of dispersed dusts by providing means to estimate the density of black liquor, means to calculate the liquid flow rate at a black liquor nozzle, means to calculate the heated temperature of the black liquor, and means to measure the viscosity. CONSTITUTION:The black liquor in a mixing tank 1 is supplied to a black liquor burner nozzle 3 that is installed on the wall face of the furnace 17 of a black liquor recovery boiler by means of a black liquor pump and jetted out into the furnace 17. The black liquor is heated to a specified temperature by a black liquor heater 2. For each kind of black liquor an estimated value 9 of the black liquor density is obtained by a black liquor specific gravity detection device 7, and based on this estimated value the black liquor viscosity setting 12 is made, and based on the set viscosity a most suitable grain diameter 11 is set. The viscosity required for obtaining this most suitable grain diameter is derived from the flow rate 10 given by the flow rate 8 of the black liquor and detected specific gravity 7, and the diameter of the nozzle used for atomizing the black liquor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device attached to a boiler that burns black liquor, which is waste liquid. The present invention relates to a device that prevents dust from scattering.

[Conventional technology]

In paper mills, a large amount of waste liquid called black liquor is discharged during the paper manufacturing process. Dumping this black liquor outside as it is causes environmental destruction and is not acceptable.

Here, black liquor is a liquid that is eluted from plant materials such as chips.
A boiler that burns black liquor because it contains flammable substances, so burning this black liquor greatly reduces its volume and facilitates post-treatment, and the heat generated by combustion is effectively used as steam. (black liquor recovery boiler) is provided. This boiler injects black liquor into the boiler furnace to instantaneously evaporate water in the high-temperature atmosphere inside the furnace, and the remaining combustibles fall to the bottom of the furnace and form combustible deposits called charbet. The structure is such that combustible components are mainly burned in this charbet.

[Problem to be solved by the invention]

In the black liquor recovery boiler with the above configuration, part of the fine particles in the sprayed black liquor and the char that forms charbet are scattered as dust, which adheres to the heat transfer surface formed on the upper part of the furnace or on the downstream tube. It often occurs that they grow and obstruct the flow of combustion gases.

The amount of dust scattered is closely related to the size of the droplets from the nozzle that injects the black liquor, and if the droplets are small, they may be re-splattered from the charbet, or they may not fall into the charbet and may fall into the furnace. This results in an increase in the amount of dust that is scattered by the upward flow.

The droplet size of black liquor depends on the configuration of the device that sprays and supplies black liquor, such as the aperture of the nozzle that sprays the black liquor, the black liquor flow rate at the nozzle, and the properties of the black liquor that is sprayed, mainly its viscosity. It will have a big impact.

FIG. 2 shows the basic configuration of a conventional control device.

That is, the black liquor discharged from the mixing tank 1 is heated by the black liquor heater 2, and is injected into the boiler furnace I7 by the black liquor burner nozzle 25. During this time, for example, the heating temperature of the black liquor is adjusted by the temperature controller 23, the concentration is estimated by the calculator 29, and the specific gravity is detected by the specific gravity detector 28, or the flow rate is measured by the flow meter 26. Furthermore, the injection pressure is detected by the pressure detector 27, and a certain degree of control is performed based on these measured data, but the control is not necessarily sufficient as described below.

In conventional control systems, the setting of the black liquor temperature, injection pressure, etc., which greatly affect the viscosity, are set based on values obtained empirically, and the set values are thereafter maintained. That is, regarding the black liquor temperature, the amount of steam, which is the heat source for the black liquor heater, is controlled so that the temperature becomes the initial setting value. In addition, the injection pressure is adjusted by changing the diameter of the black liquor nozzle depending on the load.

This device is controlled to maintain a constant value, and changes in the properties of the black liquor are not taken into account.If the properties of the black liquor change, a new set value is estimated based on the operator's experience and intuition. ,
Control is performed based on the set value. For this reason, control was not always appropriate, and it was difficult to significantly and stably reduce the amount of dust scattered.

Next, in view of the above points, a method has been proposed in which the boiling point of black liquor is calculated based on the black liquor concentration and the optimum temperature for heating black liquor is set based on this boiling point (Japanese Patent Laid-Open No. 62-29802~
No. 29806).

Compared to the above-mentioned example, this method enables control corresponding to the black liquor properties to a certain extent, so that the amount of dust scattered can be considerably reduced. However, since the heating temperature of the black liquor is determined by the boiling point of the black liquor, it is impossible to control the viscosity, which directly affects the droplet size, and the prevention of dust scattering has to be limited to a certain limit. .

[Means to solve the problem]

The present invention was constructed in order to solve the problems of the prior art shown above, and the optimum droplet size determined by the type of combustion device and black liquor properties is set as an initial setting value, and the optimum droplet size is The viscosity of the black liquor is determined to obtain the particle size, the optimum viscosity is calculated based on the black liquor flow rate and density at the nozzle part under combustion equipment operation, and the black liquor heating temperature is controlled to maintain this viscosity. .

To perform this control, we need a means to estimate the density of black liquor, a means to calculate the flow velocity at the black liquor nozzle, a means to calculate the black liquor heating temperature from the viscosity and black liquor concentration, and a means to directly and continuously measure the viscosity. The apparatus is characterized in that it has means for:

[Effect]

The viscosity of the black liquor injected into the boiler furnace can be adjusted appropriately by means of estimating the density of black liquor, means of calculating the flow velocity at the black liquor nozzle, and means of calculating the black liquor heating temperature from the viscosity and black liquor concentration. This keeps the injected black liquor particle size within an appropriate range to form a good charbet at the bottom of the furnace for combustion, and to minimize the amount of dust scattered.

〔Example〕

The present invention will be described in detail below, but as a premise, the relationship between the properties of black liquor and dust scattering will first be considered.

FIG. 3 shows the results of a test conducted by the inventors, and shows the results of testing and measuring the relationship between the flow rate of black liquor and the amount of scattered dust in the nozzle portion of black liquors having different viscosities.

As is clear from this figure, it was confirmed that when the viscosity of the black liquor is low, the amount of scattered dust is greatly influenced by the flow rate of the black liquor, whereas when the viscosity is high, the influence of the flow rate is small. Therefore, with a black liquor of high concentration, that is, high viscosity, it is difficult to appropriately control the droplet size even if only the flow rate is controlled. In recent years, the concentration of black liquor used for combustion has tended to increase.

Next, in FIG. 4, it was confirmed that in the relationship between the black liquor temperature and the amount of scattered dust, as the black liquor temperature decreases, the amount of scattered dust decreases rapidly. This is because the viscosity increases rapidly as the black liquor temperature decreases, and the droplet size increases.

As described above, it has been confirmed that controlling the viscosity of black liquor is more effective in controlling the droplet size than the conventional method of controlling the black liquor flow rate. As shown in Figure 6, the viscosity of black liquor varies depending on the type of black liquor, more specifically, depending on the solid content concentration, but as shown in Figure 5, the viscosity of any type of black liquor differs. has a close relationship with temperature; as temperature increases, viscosity decreases. Note that A to D in FIGS. 5 and 6 respectively indicate the same black liquor.

Next, regarding the particle size of the droplets, the larger the size, the better from the viewpoint of preventing dust scattering. However, an increase in the droplet size means a decrease in the droplet surface area relative to the droplet volume, and a large droplet size delays the evaporation of water in the black liquor and reduces its combustibility. Therefore, the particle size of black liquor is dust W1. It is necessary to set a value that satisfies both prevention of damage and flammability.

Examples will be described below.

In FIG. 1, first, the black liquor in the mixing tank 1 is pumped to the furnace 17 of the black liquor recovery boiler by a black liquor pump (not shown).
The black liquor is supplied to a burner nozzle 3 arranged on the wall of the black liquor, and is injected into the furnace 17 through this nozzle.

During this time, the black liquor is heated to a predetermined temperature by the black liquor heater 2, but in view of the fact that the viscosity of the black liquor is closely related to the black liquor temperature, the present invention is based on the premise of viscosity adjustment. The heater 2 heats the black liquor.

The optimum droplet size of black liquor is determined by taking into consideration both the required value from the equipment side, such as the furnace height of the combustion equipment, and the properties of black liquor, such as the type of black liquor, black liquor concentration, and flammability. be done.

In the illustrated apparatus, an estimated black liquor concentration value 9 is obtained by performing black liquor specific gravity detection 7 for each type of black liquor, and a black liquor viscosity setting 12 is performed based on this estimated value 9. Set diameter 11.

The required viscosity to obtain this optimum particle size is derived based on the following equation based on the flow rate 10 determined from the black liquor flow rate 8, the detected specific gravity 7, and the nozzle diameter used for black liquor spraying.

υ here, σ and also d3! : Average particle size of black liquor ξ: constant a: constant b: constant μ: Nozzle black liquid flow rate ρ: density υ: kinematic viscosity σ: surface tension It is.

It is certain that the viscosity of the black liquor itself to be measured can be estimated using the following equation (2), and the black liquor temperature for obtaining a predetermined black liquor particle size is calculated using the above equation (2).

η=α/T+β...■ (η: viscosity, T: absolute temperature, α, β: constants for black liquor type) Based on the above temperature setting values, the flow rate of the steam that is the heating source is controlled by the temperature controller 14. Adjust the black liquor temperature to a predetermined value in the black liquor heater 2. 5 shows the temperature detection of this black liquor.

The measured viscosity 6 becomes feedback information for correcting the temperature setting value estimated by the above-mentioned approximate expression.

Furthermore, when setting the black liquor temperature, it is necessary to avoid inhibiting the black liquor combustibility, so a lower limit value 15 of the black liquor temperature is set to prevent the black liquor temperature from falling below this value. In addition, if the black liquor temperature is too high, the water in the droplets sprayed in the furnace will evaporate too quickly and the amount of dust scattered due to rapid drying will increase, so it is necessary to set an upper limit value of 16 for the black liquor temperature. . The black liquor temperature is adjusted by setting the optimum temperature 13 in consideration of these set values.

〔effect〕

As specifically explained above, the present invention uses the optimum droplet size determined by the type of combustion device and black liquor properties as an initial setting value, and calculates the black liquor viscosity to obtain the optimum droplet size. The optimum viscosity is calculated based on the nozzle black liquor flow rate and density under the operation of the combustion device, and the black liquor heating temperature is controlled to maintain the viscosity. To perform this control, we need a means to estimate the density of black liquor, a means to calculate the flow velocity at the black liquor nozzle, a means to calculate the black liquor heating temperature from the viscosity and black liquor concentration, and a means to directly and continuously measure the viscosity. Since the device has a means for combusting black liquor at all times, it is possible to always burn black liquor in an optimal state, and the amount of scattered dust can be significantly reduced without reducing combustibility.

[Brief explanation of the drawing]

Fig. 1 is a control block diagram of a black liquor scattering prevention device showing an embodiment of the present invention, Fig. 2 is a control block diagram of a conventional black liquor injection device, and Fig. 3 shows the amount of scattered dust for each black liquor viscosity. A diagram showing the relationship between black liquor flow rate, Figure 4 is a diagram showing the relationship between black liquor temperature and scattered dust, and Figure 5 is a diagram showing the relationship between black liquor temperature and viscosity for each type of black liquor. FIG. 6 is a diagram showing the relationship between solid content concentration and viscosity for each type of black liquor. 2...Black liquor heater 3...Black liquor burner nozzle
5...Temperature detector 6...Viscosity detector 7...
・Specific gravity detector 8...Flow rate detector 9...Concentration calculator 10...Nozzle flow velocity calculator 11...
・Optimal particle size setting device 12...Viscosity setting device 13...
Temperature selector 14...Temperature regulator 17...Black liquor recovery boiler furnace No. 1 m/s) Cap diagram ('C)

Claims (3)

[Claims] (1) In an apparatus for burning black liquor by injecting it into a furnace, means for estimating black liquor concentration, means for measuring black liquor viscosity, and means for measuring black liquor temperature;
A means for measuring the black liquor jetting speed at a nozzle part, a means for calculating the black liquor viscosity to obtain the optimum droplet size of the black liquor for suppressing dust scattering, and a means for maintaining this black liquor viscosity. A dust scattering prevention device for a black liquor recovery boiler, comprising means for controlling the temperature of black liquor. (2) means for calculating the black liquor viscosity to obtain the optimum droplet size of the black liquor for suppressing dust scattering;
Dust of a black liquor recovery boiler as set forth in claim (1), characterized in that it is a calculation device whose calculation elements are the black liquor flow rate at the nozzle section during operation at the optimum black liquor viscosity, and the black liquor density. Shatterproof device. (3) Black liquor recovery according to claim 1 or 2, wherein the means for estimating the black liquor density is an arithmetic device that calculates from the measured black liquor specific gravity. Boiler dust scattering prevention device.